Controlled stress, oscillatory rheometry of mesophase-pitches Original Research Article

The rheology of mesophase-pitches, having different percentage mesophase content, has been investigated by means of controlled stress, oscillatory rheometry. Three thermally transformed mesophase-pitches (prepared from Ashland A240), with mesophase contents in the range 60–95%, together with a 100% optically anisotropic synthetic mesophase-pitch from Mitsubishi Gas-Chemical Company were studied. With the application of the time-temperature superposition principle, the viscoelastic behaviour of these mesophase-pitches was revealed in the form of the G′, G″, η′ and master curves. At high reduced frequencies (or low temperatures), all the samples behave elastically, as is typical of a glassy solid. With decreasing reduced frequency (or increasing temperature), they become viscoelastic, their behaviour tending towards that of a Newtonian fluid, i.e. simple viscous behaviour. However, elasticity returned at very low reduced frequency (or high conditions for these materials).